The present invention generally relates to a parity checking technique and, more particularly, to such a technique for detecting the failure of word lines shared by a plurality of bytes whereby all of the bits erroneously assume the value "1" or the value "0".
In the case of read only storage arrays and random access memory arrays fabricated on semiconductor chips, for example, there are the possibilities that chip word line failure or chip power distribution failure might occur which cause all of the data and parity bits stored in the addressed word line to fail to an all "1" or all "0" state. Such failures cannot be detected by conventional even or odd bit parity checking shemes implemented on a per byte basis. For example, if an event number of bits per byte and an odd bit parity checking scheme is used on a per byte basis, the all "0's" failure mode would be detected, but the all "1's" failure mode would not be detected. That is, the odd number of "1's" (an even number of data bits plus one parity bit) would produce a valid odd bit parity check. If an even bit parity checking scheme had been used in the assumed case, the reverse situation would obtain, i.e., the all "1's" failure would be detected but the all "0's" failure would not be detected.